Apparatus and method for minimizing smoke formation in a flaring stack

ABSTRACT

An apparatus and method for minimizing smoke formation in the operation of a flaring stack. The apparatus includes a generally annular gas deflector having an outer surface for deflecting the waste gas therealong. A plurality of lobes extend radially from the deflector to provide improved mixing between the waste gas, steam, and combustion air during combustion to reduce smoke formation.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/819,173 filed May 3, 2013.

FIELD OF THE INVENTION

The subject application relates to an apparatus for minimizing smokeformation in a flaring stack.

BACKGROUND OF THE INVENTION

Flare apparatus have traditionally been utilized for burning andexhausting combustible gases. Flare apparatus are commonly mounted onflare stacks and located at production, refining, and processing plantsfor disposing of flammable waste gases or other flammable gas streams,which are diverted for any reason, including but not limited to venting,shut-downs, upsets, and/or emergencies. Primarily, flare stacks are usedfor venting unwanted waste gas streams from a facility.

It is generally desirable that flammable gas be burned without producingsmoke, and reduction in smoke production during burning may be mandatedby regulatory requirements.

One method that has been adopted for reducing smoke formation duringburning includes mixing the waste gas stream to be burned with ambientair to maximize oxidation of the flammable waste gas to prevent theproduction of smoke. Another method that has been used includessupplying steam to the combustion zone, such as, for example, by aneductor to increase oxidation to restrict smoke formation. In someapplications, ambient air and steam introduction are used together tofurther reduce smoke formation.

When sufficient ambient air and/or steam is available to contact thecombustible waste gas, the mixture may be smokelessly burned. In typicalflare apparatus, only a portion of the desired amount of air and/orsteam is present for mixing with the waste gas.

A wide variety of apparatus and processes have been proposed to increasethe smokeless burning of combustible gas from a flare. For example, U.S.Pat. No. 3,833,337 to Desty et al. and U.S. Pat. No. 8,337,197 to Poe etal. propose the use of a tulip shaped Coanda tip. Coanda tips have beenused in flares with high flow rates and pressures to cause the adherenceof the waste gas to the surface. The negative pressure and viscousforces caused by the Coanda effect cause the fluid to be drawn againstthe surface in a relatively thin film, which allows proximate fluid(e.g. ambient air) to be mixed efficiently with the fluid stream. Poedescribes that to achieve a Coanda effect, the surface of the Coandasurface should be substantially smooth.

While current apparatus and methods have improved the smokelesscombustion of waste gas streams, it is desirable to further reduce theamount of smoke formation based on regulatory and environmentalconsiderations.

SUMMARY OF THE INVENTION

By one aspect, an apparatus is provided minimizing the formation ofsmoke in the operation of a flaring stack. The apparatus includes asupport arm having a generally hollow waste gas passageway forconnection to a waste gas source. The apparatus further includes agenerally annular gas deflector having an outer surface for deflectingwaste gas and steam therealong. A waste gas outlet is provided betweenthe gas deflector and the support arm. The apparatus further includes asteam distributor for distributing steam with an outlet configured todirect the steam along the outer surface of the gas deflector. The gasdeflector includes a plurality of lobes extending generally radiallyfrom the gas deflector outer surface for providing improved mixingbetween the steam, waste gas, and combustion air during combustion.

By another aspect, a method is provided for combusting a waste gas toreduce the formation of smoke. The method includes passing steam alongan outer surface of a generally annular gas deflector including aplurality of lobes extending radially outwardly therefrom. The methodincludes passing the waste gas along the outer surface of the gasdeflector, including over the plurality of lobes. The method furtherincludes drawing ambient air toward the outer surface for mixing withthe waste gas and steam and igniting the waste gas mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an apparatus including a plurality ofsupport arms and a plurality of corresponding gas deflectors inaccordance with various embodiments;

FIG. 2 is a perspective view of a support arm of the apparatus with agas deflector in accordance with various embodiments;

FIG. 3 is a cross-sectional view of the support arm of FIG. 2 with thegas deflector supported thereon in a lowered position;

FIG. 4 is a top view of the gas deflector of FIG. 2;

FIG. 5 is a side cross sectional view of the gas deflector of FIG. 4taken along line A-A;

FIG. 6 is a side cross sectional view of the gas deflector of FIG. 5taken along line B-B;

FIG. 7 is a perspective view of a support arm of the apparatus with agas deflector in accordance with another approach;

FIG. 8 is a perspective view of a steam chamber in accordance withvarious embodiments;

FIG. 9 is a perspective view of a steam chamber in accordance with otherembodiments; and

FIG. 10 is a perspective view of a steam chamber in accordance withother embodiments.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions and/or relative positioningof some of the elements in the figures may be exaggerated relative toother elements to help to improve understanding of various embodimentsof the present invention. Also, common but well-understood elements thatare useful or necessary in a commercially feasible embodiment are oftennot depicted in order to facilitate a less obstructed view of thesevarious embodiments of the present invention. It will further beappreciated that certain actions and/or steps may be described in aparticular order of occurrence while those skilled in the art willunderstand that such specificity with respect to sequence is notactually required. It will also be understood that the terms andexpressions used herein have the ordinary technical meaning as isaccorded to such terms and expressions by persons skilled in thetechnical field as set forth above except where different specificmeanings have otherwise been set forth herein.

DETAILED DESCRIPTION

The apparatus and method presented herein, in accordance with variousaspects, relates to reducing smoke formation during combustion of awaste gas in a flare stack. The apparatus may be used with a flarestack, for example, at a refinery or production facility for flaringwaste gas or other gas streams to the atmosphere. As used herein, theterm “waste gas” refers to any combustible gas stream that is combustedby the flare stack, including, but not limited to undesired gas streams,product streams combusted during shutdown or emergency situations, andother streams.

Referring now to FIGS. 1 and 2, an apparatus 2 for the combustion of awaste gas stream in accordance with various aspects is provided. Theapparatus 2 includes a gas deflector 4 for deflecting fluid along asurface 6 thereof. The apparatus also includes a steam distributor 7 fordistributing steam along the surface of the gas deflector. The apparatus2 may also include a support arm 8 for supporting the gas deflector 4thereon. One or both of the waste gas and the steam may be passedthrough the support arm 8 to the gas deflector 4. In this regard, thesupport arm 8 may have a waste gas passageway 10 and/or a steampassageway 11 formed therein, as illustrated in FIG. 3 for facilitatingthe flow of the waste gas and the steam therethrough. A waste gas outlet12 is provided for introducing the waste gas from the waste gaspassageway 10 to the gas deflector 4. A steam outlet 13 is provided fordispersing the steam from the steam passageway 11 to the gas deflector4. As illustrated in FIG. 3 and described further below, the outlets 12and 13 may include annular openings 14 and 15 respectively between thesupport arm 8 and the gas deflector 4 so that the waste gas flowsthrough the opening 14 and along the gas deflector outer surface 6. Byone aspect, the steam outlet 13 may be positioned radially inwardly ofthe waste gas outlet 12.

The waste gas deflector includes a plurality of lobes 16 that extendradially therefrom. In this regard, as steam and waste gas flow alongthe outer surface of the gas deflector 4, the steam and gas flow overand between the lobes 16. It has been identified that including radiallyextending lobes 16 on the gas deflector 4 improves mixing of the wastegas stream and the steam, and also combustion air where present duringoperation of the flare stack resulting in a reduction in the amount ofsmoke that is produced during combustion. It has further been identifiedthat including radially extending lobes 16 as described herein providesa lower flame temperature and reduced emissions of unwanted by-productsinto the atmosphere, such as NO_(X). By one aspect, the lobes 16 includea plurality of generally vertically oriented ribs 18 spacedcircumferentially about the gas deflector 4 such that the steam and gasflow along the ribs and through channels 20 formed between adjacent ribs18.

According to various aspects, the support arm 8 is provided forsupporting the gas deflector 4 thereon. The support arm 8 may alsoinclude a gas passageway 10 for passing the waste gas to be combustedfrom a gas source to the gas deflector 4. The support arm may alsoinclude a steam passageway 11 for passing steam from a steam source tothe gas deflector. In one approach, as illustrated in FIG. 1, theapparatus 2 may include a plurality of support arms 8 supporting aplurality of gas deflectors 4. In this manner, the size of each gasdeflector 4 may be decreased as opposed to having a single large gasdeflector. This may improve the ability for smoke free combustion byincreasing the amount of combustion air available for mixing with thegas at each of the plurality of gas deflectors 4 as opposed to a singlelarger gas deflector.

The support arm 8 may extend from a central plenum 22 as illustrated inFIG. 1. As shown, one support arm 8 extends upwardly from the top of theplenum 22 while additional support arms 8 extend at inclined angles fromside portions 24 of the plenum 22 and extend generally vertically atbent portions 26 thereof In one example, the vertical portions 28 of thesupport arms 8 extend vertically at an angle of less than about 5degrees from the vertical, less than about 3 degrees from the verticalaxis in another example, and at less than about 1 degree from thevertical in yet another example.

The support arm 8 may include the gas passageway 10 as illustrated inFIG. 3 for passing the waste gas through the support arm 8 toward thegas deflector 4. In one approach, as shown in FIG. 3, the gas passageway10 may include a hollow passageway through the support arm 8. In thisregard, the support arm 8 may be formed by a generally hollow tubeproviding the passageway 10. The tube may be cylindrical as illustratedin FIG. 3 or other suitable configurations.

The support arm 8 may also include the steam passageway as illustratedin FIG. 3 for passing the steam through the support arm 8 toward the gasdeflector 4. In one approach, as shown in FIG. 3, the steam passageway11 includes a tube or pipe 13 positioned within the gas distributor. Thetube 13 may run through a generally central portion of the support arm 8to form a generally annular gas passageway 12 thereabout. The steamdistributor 7 may include a steam distribution system 29, includingsteam conduits external of the support arm 8 and plenum 22 for passingthe steam into the support arm 8.

As mentioned previously, the apparatus 2 according to various aspectsincludes a gas deflector 4. In one preferred form, the gas deflector 4includes a gas deflector bowl 36 having a Coanda surface 38 asillustrated in the figures. The Coanda bowl 36 may have a tulip-shapedconfiguration as illustrated in FIG. 3 having a generally horizontallower portion 40, a vertical or inclined upper portion 42, and a convexportion 44 connecting the lower portion 40 to the upper portion 42. Theremainder of the description will be made with reference with use of theCoanda bowl 36 as the gas deflector. Coanda bowls are generally knownand understood by those of skill in the art, and are known to produce a“Coanda effect”, wherein gases flowing along the outer surface thereoftend to follow the surface forming a thin film and drawing insurrounding gas or air. In one approach, the Coanda bowl has a generallyround cross-section taken along a plane orthogonal to a longitudinalaxis 46 of the bowl, although the bowl 36 may also include othersuitable cross-sectional configurations, for example oval or polygonal.

By one aspect, the Coanda bowl 36 includes a plurality of lobes 16extending radially outwardly from its outer surface 38. As illustratedin the figures, the lobes 16 may include a plurality of generallyvertical ribs 18 spaced circumferentially about the bowl outer surface38. In one approach, the ribs extend radially outwardly from the Coandabowl outer surface 38 (or floors 20 of the channels). As used herein,the phrase “total outer surface” refers to the outer surface formedalong all outer surface of the gas deflector, including by one examplealong the outer surfaces of the Coanda bowl 36, ribs 18, and channels20, such that the “total outer surface” of a ribbed portion of theCoanda bowl 36 has a larger surface area than the outer surface of acorresponding Coanda bowl without ribs.

According to one approach, the ribs 18 extend generally vertically alongthe Coanda bowl outer surface 38. It should be understood that asdescribed herein, the ribs 18 extend generally vertically as viewedhead-on and that where the upper portion 42 of the bowl 36 is inclinedas illustrated in FIG. 5, the vertically extending ribs may similarly beinclined toward the longitudinal axis 46 of the bowl 36 when viewed fromprofile (i.e. 90 degrees from head-on as shown by the side-cross sectionof FIG. 5). With this in mind, by one approach, the ribs have agenerally vertical axis 48 when viewed head-on as shown in FIG. 2 thatis less than about 5 degrees from vertical in one example, less thanabout 2 degrees in another example, and less than about 1 degree fromvertical in yet another example.

The ribs are circumferentially spaced so that a plurality ofcorresponding channels 20 are formed between adjacent ribs 18 asillustrated in FIG. 2. The channels 20 extend generally verticallybetween the ribs 18 and can have a variety of different shapes andconfigurations. The channels 20 include a channel floor 50 at a basethereof The channel floor 50 may be flush with the Coanda bowl outersurface 36, or may be raised or indented relative thereto.

The ribs 18 may have a generally constant radial profile (i.e. distancethe ribs extend from the bowl outer surface 36 and/or channel floor 50).Alternatively, the ribs 18 may have a varying radial profile asillustrated in FIG. 5. By one approach, as seen in FIGS. 2 and 5, theribs 18 are tapered from a lower rib portion 52 to raised rib portion54. In this regard, the tapered lower portion 52 may be slightlyelevated with respect to, or flush with, the bowl surface 36 to providea smooth transition surface over which steam and gas traveling upwardlytherealong can flow. The ribs 18 may also include a tapered upper ribportion 56 to provide for smooth flow of the steam, waste gas andcombustion air mixture as it exits the Coanda surface. It should beunderstood that the radially extending ribs may be radially extendingrelative to an outer surface of a Coanda bowl and/or relative tochannels.

In this regard, the ribs may be formed, for example by providing ribsalong the outer surface of a Coanda bowl, or by forming channels orindentations in a Coanda bowl so that the ribs are formed above thechannels.

The ribs may have a constant circumferential width or a varying widthabout the perimeter of the Coanda bowl 36 as illustrated in FIG. 2.Similarly, the channels 20 may have a constant or varyingcircumferential width. Typically, where the Coanda bowl includes aninwardly tapered upper portion 42 as illustrated, at least one of theribs and channels will have a varying width to account for the upwardlydecreasing circumference.

By one aspect, the ribs 18 may have inclined sidewalls 58 extendingbetween rib top portions 60 and the channel floors 50 as best seen withreference to FIGS. 3 and 5. The inclined sidewalls 58 can be generallyflat, or may be curved or formed in other manners. The inclined sidewalls 58 provide a smooth surface over which the steam and gas can flowby reducing the amount of sharp angles between the ribs and thechannels.

Without intending to be bound by theory, it is believed that theaddition of ribs 18 to the Coanda bowl 36 increases the total surfacearea of the Coanda bowl 36 to improve mixing of the steam and waste gas,and also combustion air when it is present, without providing acorresponding increase in outer diameter of the bowl. In this manner,the Coanda bowl 36 can advantageously be kept relatively small whileproviding sufficient surface area for mixing of the steam, gas andcombustion air reducing smoke formation.

To this end, by one aspect, the ribbed Coanda bowl has a relatively highratio of a perimeter (as shown in FIG. 4) to an outer radius 62. As usedherein, outer radius refers to the distance between the bowllongitudinal axis 46 and the rib top portions 60. For example, atraditional un-ribbed Coanda bowl has a ratio of perimeter(circumference) to outer radius of 2 πr/r=2 π. In one example, the ratioof the perimeter to the outer radius of the ribbed bowl described hereinis greater than 2 π. In another example, the ratio of perimeter to outerradius is between about 6.5 and about 20, between about 7.5 and about 16in another example, and between about 8.5 and about 12 in yet anotherexample.

According to one aspect ribs 18 may be formed along the entire outersurface 38 of the Coanda bowl 36. In this regard, the surface area ofthe entire bowl 36 is increased such that mixing between the steam,waste gas and the combustion air is improved along the total outersurface as described above.

According to another aspect, the ribs 18 may extend along one or moreportions of the Coanda bowl 36, but less than the full outer surface 38thereof, such that a portion of the gas deflector is unribbed andprovides a relatively smooth surface for gas flow. For example, asillustrated in FIG. 2, the lower portion 40 and/or the intermediateportion 44 of the Coanda bowl 36 may be unribbed, while an upper portion42 includes ribs. In this regard, gas may better flow along the lowerportion 40 of the Coanda bowl 36, along the convex intermediate portion44, and to the ribbed upper portion 42 before flowing over and betweenthe ribs 18. In one example, between about a bottom 5 to 50 percent ofthe Coanda bowl is unribbed with an upper portion including ribs. Inanother example between about a bottom 10 to 40 percent of the Coandabowl is unribbed with an upper portion including ribs. In anotherexample, as illustrated in FIG. 7 a bottom portion may include ribs withat least an intermediate portion and/or a top portion being unribbed.

As illustrated in FIGS. 2 and 7, different numbers and sizes of ribs 18may be included on the Coanda bowl to maximize the steam/wastegas/combustion air mixing. For example, it may be beneficial to selectthe number of ribs extending circumferentially about the Coanda bowl 36to provide increased surface area and the associated improvement insteam/gas mixing, while still ensuring that the steam and gas will flowsmoothly over the total surface area during operation. FIG. 2illustrates an example of a Coanda bowl 36 that includes a smallernumber of relatively wider ribs 18 while FIG. 7 illustrates anotherexample where a larger number of narrower ribs 18 are used. With this inmind, in one example a ratio of a combined circumferential width of theone or more ribs 18 to a combined circumferential width of a pluralityof channels 12 between the ribs 18 is between about 0.5 and about 5 andbetween about 1 and about 3 in another example. In another example, aratio of a rib radial height above the channel floor to the outer radiusof the bowl is between about 0.01 and about 0.2 in one example andbetween about 0.03 and about 0.2 in another example.

As mentioned previously, by one aspect, a steam outlet 13 is providedfor introducing the steam toward the outer surface of the Coanda bowl.With reference to FIGS. 2 and 3, the steam outlet may include agenerally annular opening 15 of the steam passageway extending about thelongitudinal axis of the Coanda bowl 36 for distributing the steam alongthe surface thereof The annular opening 15 may be formed of a singleopening, or a plurality of smaller openings as illustrated in FIGS. 2and 3. By one approach, the steam outlet 13 includes a steam disperser70 as illustrated in FIG. 3. The steam disperser may be formed in avariety of different configurations. As illustrated, the steam disperser70 includes an inverted frusto-conical chamber 72 having a narrowerbottom portion 74 and a broader top portion 76. One or more chamberopenings 78 are formed about the perimeter of the top portion 76 toprovide the annular opening 15 for dispersing the steam. In this manner,steam may be dispersed from the generally central steam passageway 11along the surface of the Coanda bowl 36.

As illustrated in FIG. 8, by one approach, the chamber 72 includes upperapertures 80 formed through the top portion 76 of the chamber formingthe chamber openings 78. By one aspect, as illustrated in FIGS. 9-10,the chamber 72 includes a notched upper rim portion 82. In this regard,with the chamber 72 in position below the Coanda bowl 36, the openingsare formed between the Coanda bowl outer surface 38 and indentations 84formed in the notched upper rim portion Various configurations arepossible for the notched upper rim portion 82. In one example, asillustrated in FIG. 9 the notched upper rim portion includes serrations86 providing a saw tooth appearance with triangular openings formedbetween the Coanda bowl 36 and the serrations 86. By another approach,the notched upper rim portion may be formed of alternating crenels 88and merlons 90 as illustrated in FIG. 10 to form openings between thecrenels and the Coanda bowl 36.

By one aspect, the openings 78 may be aligned with the ribs 18 toprovide for increased flow of steam over the ribs 18. By anotherapproach, the openings 78 may be aligned with the channels 20. By yetanother approach, openings may be aligned with both the ribs and thechannels or may be offset relative to one or both.

As mentioned, by one aspect, the gas outlet 12 is provided forintroducing the waste gas toward the outer surface of the Coanda bowl.As illustrated in FIGS. 2-3, the gas outlet 12 may include a generallyannular opening 14 of the waste gas passageway 10 formed about the outersurface 38 so that the waste gas can flow through the opening and alongthe outer surface. The annular opening 14 may include a relatively roundshape, or another shape, such as an oval or polygon. By one approach,the annular opening includes a single annular opening, but may alsoinclude a plurality of openings formed about the Coanda bowl 36. Theannular opening 14 may be formed by a gap between the support arm upperseating portion 30 and the Coanda bowl lower portion 40, such that wastegas flowing through the gas passageway 10 exits through the opening 14and flows along the outer surface 38.

According to one aspect, the gas outlet 12 is provided radiallyoutwardly of the steam outlet 13 as illustrated in FIGS. 2 and 3. Inthis manner, steam is directed along outer surface 38 and the waste gasis directed toward the outer surface 38 and the steam flowing thereover.Not to be bound by theory, it is believed that by forming the gas outletradially outwardly of the steam outlet 13, a thin layer of steam isformed over the outer surface 38 of at least a portion of the Coandabowl 36. The waste gas is directed toward the steam and forms a layer ofwaste gas flowing along the layer of steam. Combustion air may then beavailable radially outwardly of the waste gas layer. In this manner, asthe steam and gas stream flow over the ribbed surface of the Coandabowl, 36 improved mixing may occur as the waste gas layer is contactedby the steam on one side and the combustion air on the other side,resulting in reduced smoke formation during combustion.

According to various aspects, during operation, the steam flows throughthe steam passageway 11 and through the annular opening 15 along theCoanda bowl outer surface 38. The waste gas to be combusted flowsthrough the gas passageway 10 and through the annular opening 14. As thesteam and waste gas flow along the outer surface 38, they mix togetherand may further mix with combustion air (for example surrounding ambientair) that is drawn toward the waste gas and steam and mixed therewith.The steam and waste gas pass over the ribs 18 and through the channels20 therebetween. The mixture is ignited and combusted with reduced smokeformation.

The above description and examples are intended to be illustrative ofthe invention without limiting its scope. While there have beenillustrated and described particular embodiments of the presentinvention, it will be appreciated that numerous changes andmodifications will occur to those skilled in the art, and it is intendedin the appended claims to cover all those changes and modificationswhich fall within the true spirit and scope of the present invention.

1. An apparatus for minimizing the formation of smoke in the operationof a flaring stack, the apparatus comprising: a support arm having agenerally hollow waste gas passageway for connection to a waste gassource; a generally annular gas deflector having an outer surface fordeflecting waste gas; a waste gas outlet between the gas deflector andthe support arm; a steam distributor for distributing steam; an outletof the steam distributor configured to direct steam along the outersurface of the gas deflector; and a plurality of lobes extendinggenerally radially from the gas deflector outer surface for providingimproved mixing between the steam, waste gas, and combustion air duringcombustion.
 2. The apparatus of claim 1, wherein the gas deflectorincludes a tulip-shaped Coanda bowl.
 3. The apparatus of claim 1,wherein the lobes include circumferentially spaced generally verticalribs extending radially from the outer surface of the gas deflector. 4.The apparatus of claim 3, wherein the steam distributor includes anannular outlet positioned about the annular gas deflector for directingsteam therealong.
 5. The apparatus of claim 4, wherein the steamdistributor annular outlet includes a plurality of circumferentiallyspaced openings positioned about the annular gas deflector.
 6. Theapparatus of claim 5, wherein the openings are generally aligned withthe ribs.
 7. The apparatus of claim 5, wherein the openings aregenerally aligned with channels formed between the ribs.
 8. Theapparatus of claim 4, wherein the waste gas outlet includes a generallyannular outlet positioned radially outwardly of the steam distributor.9. The apparatus of claim 3, wherein a ratio of a perimeter of a ribbedportion of the bowl to an outer diameter of the ribbed portion isbetween about 6.5 and about
 20. 10. The apparatus of claim 3, whereinthe ribs are tapered radially with respect to the outer surface from agenerally lower rib portion flush with the outer surface to a raised ribportion above the outer surface.
 11. The apparatus of claim 3, whereinthe ribs include inclined sidewalls extending from channels between theribs to upper raised rib portions.
 12. An apparatus for minimizing theformation of smoke in the operation of a flaring stack, the apparatuscomprising: a support arm having a generally hollow waste gas passagewayfor connection to a waste gas source; a generally annular gas deflectorhaving an outer surface for deflecting waste gas; a waste gas outletbetween the gas deflector and the support arm; a steam distributor fordistributing steam; a plurality of circumferentially spaced generallyvertical ribs extending radially from the gas deflector outer surfacefor providing improved mixing between the steam, waste gas, andcombustion air during combustion; and a generally annular outlet of thesteam distributor configured to direct steam along the outer surface ofthe gas deflector.
 13. The apparatus of claim 12, wherein the supportarm includes a steam passageway positioned within the waste gaspassageway.
 14. The apparatus of claim 12, wherein the steam distributorincludes a steam chamber and the steam chamber outlet includes pluralityof upper openings.
 15. The apparatus of claim 14, wherein the steamchamber includes an inverted generally hollow frustoconical member withthe upper openings about an upper portion thereof
 16. The apparatus ofclaim 14, wherein the steam chamber upper openings include a notchedupper rim adjacent to a bottom portion of the steam distributor.
 17. Theapparatus of claim 14, wherein the steam chamber upper openings includea plurality of apertures about the upper portion of the steam chamber.18. The apparatus of claim 14, wherein the upper openings are generallyaligned with the ribs.
 19. The apparatus of claim 14, wherein the upperopenings are generally aligned with channels between the ribs.
 20. Theapparatus of claim 12, wherein the waste gas outlet is generally annularand positioned radially outwardly of the steam distributor outlet toprovide steam along the outer surface of the gas deflector.